Method of laminating packaging film

ABSTRACT

A multiple layer laminated packaging film incorporating cellophane coated on only one side with a heat sealable coating, heat sealable polyethylene applied to the uncoated side of the cellophane, and a polypropylene exterior layer joined to the coated side of the cellophane by means of a heat sealable coating on the inner surface of the polypropylene.

United States Patent [1 1 Paisley et al.

METHOD OF LAMINATING PACKAGING FILM Inventors: George C. Paisley,Millbrae; Fred G.

Tier, Sunnyvale, both of Calif.

Assignee: Milprint, Inc., Milwaukee, Wis.

Filed: Mar. 8, 1971 Appl. No.: 122,205

Related US. Application Data Continuation of Ser. No. 717,844, March 1,1968, abandoned.

US. Cl l. 156/280, 156/244, 156/308, 156/314,156/331,161/190,161/227,

Int. Cl B32b 31/06, B32b 31/12 Field of Search 161/254, 249' [1113,784,434 [451 Jan. 8, 1974 [56] References Cited UNITED STATES PATENTS3,037,868 6/1962 Rosser 161/249 3,445,324 5/1969 Curlertal.,............. ,1614254 Primary Examiner-Clifton B. CosbyAtt0rneyD0nald G. Casser 57 ABSTRACT A multiple layer laminatedpackaging film incorporating cellophane coated on only one side with aheat sealable coating, heat scalable polyethylene applied to theuncoated side of the cellophane, and a polypropylene exterior layerjoined to the coated side of the cellophane by means of a heat sealablecoating on the inner surface of the polypropylene.

1 Claim, 1 Drawing Figure POLYPROPYLENE- WITH HEAT SEAL COATING POLYETHYLENE CELLOPHANE WITH HEAT S EAL COATING PATENTEDm m 3,784,434

POLYPROPYLENEE WITH HEAT SEAL COATING POLY ET HYLENE CELLOPHANE WITHHEAT 5 EAL comma T INVENTORS FRED 6. TIER G ORGE C. PAISLEY ATTORN EVMETHOD OF LAMINATING PACKAGING FILM This application is a continuationof Ser. No. 717,844, filed Mar. 1, 1968, now'abandoned.

BACKGROUND OF THE INVENTION 1. Field The field of the present inventionis the art of packaging films, more specifically multiple layerlaminated films which can be wrapped around an object to be packaged orconverted into containers such as bags or pouches in which articles canbe inserted.

2. Prior Art Laminated films incorporating saran coated cellophane,polyethylene and polypropylene are known in the prior art. An example ofone known construction of this general class is shown in U. S. Pat. No.3,274,004 in which a polypropylene first layer is joined to apolyethylene second layer which in turn is joined to a cellophane thirdlayer coated on both sides with saran and then a polyethylene fourthlayer is joined to the opposite side of the double coated cellophanelayer. The film thus involves four film layers and two layers of sarancoating, which is a large number of lay ers and can increase the expenseof its manufacture, and the cellophane layer is coated on both sideswith a barrier material, i.e., the saran coatings, thereby preventingthe cellophane layer from being moisturized during the processofmanufacturing the film.

SUMMARY OF THE INVENTION The present invention simplifies the mechanicalconstruction of a multiple layer film laminated packaging filmincorporating coated cellophane, polypropylene and polyethylene. In thefilm construction of this invention, a polypropylene first layer isjoined to a cello phane second layer that is coated on only one sidewith saran, the polypropylene being joined to the saran coated side ofthe cellophane through the use of a heat sealcoating on thepolypropylene, and a polyethylene layer is joined to the uncoatedsurface of the cellophane.

From the foregoing description of the films of this invention, it can beseen that several layers have been eliminated as compared to the priorart film mentioned above. The present construction involving a reducednumber of layers is believed to provide a packaging film which is lessstiff than the prior art film, thereby imparting greater machineabilityto the finished film, by which is meant that it is easier to employ thefilm on a packaging machine which may form or wrap the film about anarticle to be packaged. Further, the decrease in the number of layersimproves the ability of the laminated film to form around a productbeing packaged on automatic packaging machinery, thereby providing amore tightly-conforming package.

Secondly, incorporation of a cellophane layer having a saran coating ononly one of its surfaces as compared to a cellophane layer having asaran coating on both of its surfaces as in the above prior art filmleads to a very important advantage. Because the cellophane layer isfirst joined to the polypropylene layer along its saran coating, itsopposite surface is left exposed after the lamination has taken placeand before the inner polyethylene layer is joined to the uncoatedsurface of the cellophane. This allows the film laminator to applymoisture to the hydrophilic cellophane layer, thereby enabling him toincrease its moisture content. Because 2 the plasticity of thecellophane (regenerated cellulose) is proportional to its moisturecontent, this greatly increases the softness and pliability of thelaminated film material. In the prior art film mentioned above, sincethe cellophane is coated on both sides with saran, there is noopportunity to apply moisture to the hydrophilic cellophane layerbecause the saran is a barrier coating for water or water vapor.

As another feature of the present invention, the heat sealable coatingon the polypropylene and the heat sealable coating on the cellophane areboth to have a relatively low sealing temperature range on the order ofF to 250F in order that joinder of the polypropylene to the cellophanelayer can be accomplished with a minimum risk of thermal damage toeither the cellophane or the polypropyleneThis is in contrast to someprior art films wherein polypropylene is joined to coated cellophane bymeans of a layer of molten polyethylene that has been extruded at atemperature around 600F. This is an especially important feature becauseit reduces wrinkling or curling of the polypropylene which, in mostapplications of the present film, will form the exterior layer of awrapped article. If the polypropylene is an oriented film, the low heatsealing temperature will also lessen any potential adverse effects ofheat thereupon.

The laminated packaging films of this invention are useful in any of thenormal packaging applications, such as for packaging food items ornon-food items; however, it has proved effective as a wrapping materialfor cheese, particularly where it is wrapped about cheese in aform-andfill package that is filled or flushed with an inert gas beforethe wrapper is completely sealed.

DESCRIPTION OF THE DRAWING The ensuing description teaches theprinciples of the present invention by means of an illustrativeembodiment and a discussion of some possible variations; the descriptionis made with reference to the accompanying drawing which shows aperspective view, on an enlarged scale, of a sheet of laminatedpackaging film made according to the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The drawing illustrates onefilm of the present invention, and depicts a sheet 10 of wrappingmaterial having the following construction:

1. A first layer 11 of heat-seal coated polypropylene consisting of apolypropylene substrate film l2 having a heat sealable coating 13 on oneof its surfaces, the heat sealable coating 13 being applied to thepolypropylene substrate before the layer 1 1 is laminated to the otherlayers of the sheet 10',

2. A second layer 14 comprising a layer of cellophane film 15 coated ononly one of its surfaces with a heat sealable coating 16 in which theheat sealable coating 16 is applied to the cellophane substrate 15before the second layer is joined with the other layers of the sheet 10;and i 3. A third layer 17 of polyethylene which is applied to theuncoated surface of the second layer 14, i.e., to the uncoated surfaceof the cellophane layer 15 opposite from its surface carrying the heatsealable coating 16.

3 The coatings 13 and 16 should be heat sealable within a temperaturerange of 180F-250F, within which broad range 190F-2l0F is especiallyeffective; they may be either the same or different compositionsprovided that they are compatible with each other if they havedissimilar compositions.

In manufacturing a sheet of laminated packaging film, the heat sealcoated polypropylene first layer 11 is first laminated to the heat sealcoated second layer 14 of cellophane with the heat seal coating 12 onthe first layer contacting the heat seal coating 16 on the second layer;upon completion of this first laminating step, the uncoated surface ofthe cellophane layer 14 remains exposed. This enables moisture, mostusefully in the form of steam applied by any suitable means with anattachment to the laminating apparatus, to be applied to the cellophanelayer through its exposed uncoated surface. Thereafter, the polyethylenethird layer 17 is applied to the uncoated surface of the cellophanesecond layer 14, in which the polyethylene may be applied by extrusioncoating or laminating a preformed film of polyethylene; suitableadhesion promoting primer coatings as are well known in the convertingart (e.g., polyalkylene imines such as polyethylene imine) may beapplied to the exposed cellophane surface after it has been moisturizedin order to enhance the bond of the polyethylene to the cellophane.Thereafter the completed material is aged as necessary to increaseadhesion of the polyethylene to the cellophane.

The following specific examples will further elucidate the nature of thepresent invention.

EXAMPLE 1 A sheet of 60 gauge biaxially oriented polypropylene coated onone side with a heat sealable coating comprising essentially saranpolymer was passed through an oven at a temperature of l60F-l80F topreheat the film. The film was then advanced to a nip roll assembly andthere combined with a sheet .of 250 R80 cello phane having a heatsealable coating comprising saran polymer on one of its surfaces. At thenip roll assembly, the sheet of polypropylene was backed up on itsuncoated side with a rubber covered roll and the cellophane sheet wasbacked up on its uncoated side with a steam heated metal roll having asurface temperature of 190F-200F and the polypropylene and cellophanesheets were laminated together under sufiicient pressure with the sarancoated surface of the polypropylene in contact with the saran coatedsurface of the cellophane so that the two fused together to form a firmbond. This laminated assembly was then led to an extrusion coater forthe application of the polyethylene third layer, but prior to suchapplication steam was applied to the exposed uncoated surface of thecellophane layer by passing the web about 3 to 6 inches from a drilledpipe that uniformly metered steam onto the web. After the application ofsteam, a polyethyleneadhesion promoting primer comprising apolyesterpolyurethane admixture was applied at a rate of about 0.5 to0.7 pounds per ream (3,000 square feet). The primer was dried, ahd heatsealable polyethylene was then extrusion coated onto the primed butotherwise uncoated surface of the cellophane at a weight of 28.8 poundsof polyethylene per ream. The material was then rewound and aged for 48hours to allow full development of the maximum adhesion of thepolyethylene to the cellophane surface.

Film according to Example 1 was used to package cheese on a commercialform-and-fill type of packaging apparatus (a Hayssen model RT machine).it was found that the film exhibited excellent machineability in that itwas very flexible and provided a wrapper that tightly conformed to theexterior of the packaged cheese. In comparison to a prior art filmlaminate including (l) polypropylene, (2) polyethylene, (3) two sidecoated cellophane, and (4) polyethylene joined together in theenumerated sequence, the film of Example l was markedly less stiff andmore readily conformed to the product when an internal partial vacuumwas formed within the package. Furthermore, shipping tests wereperformed with packaged samples using both films in which the packageswere trucked over a trip of several hunderd miles; it was found thatcheese packaged in the film of Example 1 exhibited a substantially andsignificantly lower number of leaking packages (that is, packages thathad lost the internal partial vacuum therewithin) than cheese packagesutilizing the prior art film mentioned above.

EXAMPLE 2 Another film according to this invention was manufacturedstarting with an uncoated sheet of 50 gauge biaxially orientedpolypropylene. The uncoated polypropylene film was in-line coated on thelaminating apparatus as described in Example 1 with a saran polymer heatsealable coating, heat scalable within the range of 188F to 250F; thecoating comprised a mixture of about 15 parts saran, 14 parts polyester,8 parts polyurethane and methyl ethyl ketone and ethyl acetate, withless than 1 part camauba wax. The coating was dried and thereafter thesaran coated polypropylene film was joined to the saran coating ofone-side saran coated cellophane using the process described above underExample 1. Combination of the coated polypropylene film to the coatedcellophane film was accomplished with a temperature of 190F at a fate of250 feet of film per minute. The film of Example 2 also proved to be ahighly satisfactory packaging film, exhibiting properties similar to thefilm of Example 1.

EXAMPLE 3 Using the methods described in Example 1, another satisfactorylaminated packaging film was manufactured using the same one-side sarancoated polypropylene and the one-side saran coatedcellophane but withthe polyethylene third layer applied at a coating weight of 36 poundsper ream of base film. The film was tested for its physical propertiesand found to exhibit excellent tensile strength, a broad range of heatsealing temperatures and also formed excellent packages on aform-and-fill type of packaging machine.

As mentioned in the preceding description, the first layer of themultiple layer packaging film of this invention is to comprise a film ofpropylene polymer. The term propylene polymer as used herein refers tohomopolymers of propylene, interpolymers of propylene with othercopolymerizable alpha olefins such as ethylene, butene-l etc.,containing at least 50 percent propylene, or blends containing majoramounts of the foregoing propylene homopolymers or interpolymers andother polymeric or resinous ingredients. For most packaging uses, thefirst layer may be from 50 to 1 10 gauge, that is 0.0005 inches to 0.0011 inches, thick and it may be un-oriented, uniaxially oriented orbiaxially I oriented.

The second layer of the composite films is to include a cellophane basefilm, the term cellophane being used herein to refer to films derivedfrom regenerated cellulose and cellulose ethers. The regeneratedcellulose films may be prepared by the well-known viscose process, fromcuprammonium solutions, or by regenerating cellulose from celluloseethers or esters. Cellulose ethers which may be used as a base sheetinclude hydroxyalkyl ethers, particularly hydroxy ethyl cellulose; alkylethers such as methyl and ethyl cellulose; and carboxyalkyl ethers suchas carboxymethyl cellulose. For most packaging purposes, the cellophanesecond layer may be from 140 to 250 yield (i.e., 14,000 to 25,000 squareinches/pound).

The heat sealable coatings on the one surface of the cellophane secondlayer and, in a presently-preferred form, the heat sealable coating onthe propylene first layer may both comprise a coating of saran polymer.The term saran polymer is defined herein as homopolymers andinterpolymers of vinylidene chloride having high impermeability tovapors, the commercial sarans generally comprise a binary or ternaryinterpolymer having 50 percent or more vinylidene chloride and thebalance two or more copolymerizable monomers such as vinyl chloride,alkyl methacrylates and acrylates, acrylonitrile, and acrylic acid ormethacrylic acid. Other saran interpolymers of vinylidene chloride mayalso be employed, particularly those containing at least 25 weightpercent of vinylidene chloride in the polymerized molecule and thebalance one or more other monoethylenically unsaturated monomers thatare copolymerizable with vinylidene chloride.

The third layer of the composite films of this invention is to comprisea heat sealable layer of ethylene polymer. Most generally, this can be alow density branched chain polyethylene, but in other instances a mediumdensity polyethylene may also be employed depending .on whether the heatsealing temperature range is suitable for the intended application.Polyethylene with a density of 0.918 to 0.926 and a melt index of 1.0 to15.0 applied at a weight of 14.4 to 45.0 lbs/ream (3,000 square feet) ofcellophane is effective for the purposes of this invention. When wrappedabout a package, seals may be formed between contacting portions ofpolyethylene third layers or between the polyethylene third layer andanother film or layer of the composite film.

Heat sealing as used herein refers to the character istic of softeningor fusing to form a satisfactory bond between contacting portions ofmaterial upon the momentary application of heat and pressure. Thetemperatures employed are above the softening temperature of the film orcoating being heat sealed, the pressures may vary between less than 1pound to 50 pounds per square inch, and the dwell time during which thecontacting material is subjected to the heat and pressure is normallyfrom a fraction of a second to several seconds.

It is to be understood that it is intended to cover all changes andmodifications of the examples of this invention herein disclosed, aswell as other embodiments not disclosed, which do not constitute adeparture from the true spirit and scope of this invention.

We claim:

1. A method for the manufacture of a flexible packaging film comprisingthe steps of:

1. providing a first layer consisting essentially of a film of propylenepolymer and a heat sealable saran polymer coating on a surface of thefilm, said coating being heat sealable within a temperature range ofabout 250F;

2. providing a second layer consisting of a film of cellophane and aheat sealable saran polymer coating on only a first surface of the film,said coating being heat sealable within a temperature range of about180250F, and said cellophane having an un coated second surface oppositethe first surface;

3. joining the first layer to the second layer by placing the heatsealable coating of the first layer into contact with the heat sealablecoating of the second layer and applying heat to the uncoated secondsurface of the cellophane to cause the heat sealable saran polymercoating of the first layer to fuse with the heat sealable saran polymercoating of the second layer to thereby laminate the first layer to thesecond layer;

4. moisturizing the cellophane by the application of water vapor throughits uncoated second surface after the first layer has been joined to thesecond layer but before a third layer is joined to the second layer;

5. coating said second surface of the cellophane with an adhesionpromoting primer, and

6. thereafter applying a third layer consisting of a heat sealablepolyethylene over the entire second surface of the cellophane.

2. providing a second layer consisting of a film of cellophane and aheat sealable saran polymer coating on only a first surface of the film,said coating being heat sealable within a temperature range of about180*-250*F, and said cellophane having an uncoated second surfaceopposite the first surface;
 3. joining the first layer to the secondlayer by placing the heat sealable coating of the first layer intocontact with the heat sealable coating of the second layer and applyingheat to the uncoated second surface of the cellophane to cause the heatsealable saran polymer coating of the first layer to fuse with the heatsealable saran polymer coating of the second layer to thereby laminatethe first layer to the second layer;
 4. moisturizing the cellophane bythe application of water vapor through its uncoated second surface afterthe first layer has been joined to the second layer but before a thirdlayer is joined to the second layer;
 5. coating said second surface ofthe cellophane with an adhesion promoting primer, and
 6. thereafterapplying a third layer consisting of a heat sealable polyethylene overthe entire second surface of the cellophane.